142 MAN, THE ANIMAL 



regularly exercised? Is the mind occupied and 

 contented? Such factors have a large influence in 

 enabling man to resist the poisons given off by 

 germs after they gain access to the body. 



In the illustration given of diphtheria, it was 

 shown that man might become accustomed to these 

 poisonous products and that his cells probably 

 produced a neutralizing antitoxine. In other 

 words, the body adjusted itself to a new or unusual 

 condition. This is a relation which living proto- 

 plasm is able to undertake, wherever living proto- 

 plasm is found. It is everywhere apparent in 

 nature. Fig. 47 shows a spruce tree which has 

 tipped partly over, due to the undermining in- 

 fluence of the high water. The tip of the tree 

 has adapted itself to this new position. Two of 

 the limbs have become tree-like in their symmetry 

 and bear cones. This is an adaptation taking 

 place in nature in which part of the tree under- 

 went a radical modification in attempting to adjust 

 Itself to new conditions. This is especially notice- 

 able in the tree-like symmetry of the two limbs — 

 a condition never seen while the tree stands in an 

 upright position. 



In this discussion of the scientific principles con- 

 nected with diseases caused by animals and plants, 

 a few generalizations have become clearly defined: 



I. Theoretically all of them are preventable. 



